How to fix this error?

Cell contents reference from a non-cell array object.

e = cell2mat(TI(q).Si);

TI is repmat

Si is element of TI class cell

[dpb]

"TI is repmat"

What on earth does that mean?

"How to fix?"

Don't use cell2mat on a non-cell object.

Whatever it is, which we have no way in the world of knowing, TI(q).Si is NOT a cell.

Show us what

whos TI

returns and mayhaps we can tell you something.

Syntax looks like it is a struct, maybe.